1. Field of the Invention
This invention relates to the measurement of the velocity of a moving substance by the use of nuclear magnetic resonance (NMR). In particular, this invention relates to the quantitative determination of the flow rates of flowing fluids across a given plane, and of the position dependence of such flow rates in the plane itself. The method requires no intrusion into the fluids or the surrounding matter by other than a large amplitude static magnetic field, a small amplitude radio frequency electromagnetic field, and pulsed small amplitude magnetic field gradients. Although useful for a broad range of applications, this invention finds particular utility in the field of medical diagnostics, and most particularly in the detection and measurement of blood flow rates in living animals and humans.
2. Description of the Prior Art
Techniques for the study of flowing fluids using nuclear magnetic resonance have been known for approximately 25 years. Such techniques generally involve the use of downstream detectors, saturation followed by inflow of unsaturated material, or the imposition of a field gradient to cause measurable frequency and phase shifts.
Descriptions of these techniques are found in the following papers:
J. R. Singer, "Blood Flow Rates by Nuclear Magnetic Resonance Measurements", Science 130: 1652 (1959); PA0 J. R. Singer, "Flow Rates by Nuclear and Electron Paramagnetic Resonance Methods", J. Appl. Phys., 31: 125 (1960); PA0 T. P. Grover, "NMR Flow Measurements", Ph.D. Dissertation, University of California, Berkeley, Dept. of Electrical Engineering and Computer Sciences (1971); PA0 T. Grover et al., "NMR Spin-Echo Flow Measurements", J. Appl. Phys., 42: 938 (1971); PA0 A. N. Garroway, "Velocity Measurements in Flowing Fluids by NMR", Journal of Physics D: Applied Physics, 7; L159 (1974); PA0 J. R. Singer et al., "Recent Measurements of Flow Using Nuclear Magnetic Resonance Techniques", Modern Developments in Flow Measurement, G. C. Clayton, ed., Peter Peregrinus Ltd., London (1972) pp. 38-48; PA0 P. A. Jager, et al. "Novel Method for Determination of Flow Velocities with Pulsed Nuclear Magnetic Resonance", Rev. Sci. Instr., 49(8), (1978); PA0 D. W. Jones et al., "NMR in Flowing Systems", Advances in Magnetic Resonance, Volume 8, J. S. Waugh, ed., Academic Press, N.Y. (1976); PA0 L. F. Latyshev et al., "Nuclear Magnetic Resonance in a Flowing Liquid", Moscow: Atomizdat (1968); PA0 K. J. Packer, "The Study of Slow Coherent Molecular Motion by Pulsed Nuclear Magnetic Resonance", Molecular Physics, 17: 355 (1969); PA0 J. S. Battocletti, et al., "NMR Detection of Low Magnetization Levels in Flowing Fluids", I.E.E.E. Transactions on Magnetics, Vol. Mag. 9: 451 (1973); PA0 R. E. Halbach, et al., "Cylindrical Crossed-Coil NMR Limb Blood Flowmeter", Rev. Sci. Inst., 50 (4), (1979); PA0 O. C. Morse et al., "Blood Velocity Measurements in Intact Subjects", Science, 170: 440 (1970). PA0 Lauterbur, "Image Formation by Induced Local Interaction: Examples Employing Nuclear Magnetic Resonance", Nature, 242: 190 (1973); PA0 Damadian et al., "Focusing Nuclear Magnetic Resonance (FONAR), Visualization of a Tumor in a Live Animal", Science, 194: 1430-2 (1976); PA0 Hinshaw et al., "Display of Cross-Sectional Anatomy by Nuclear Magnetic Resonance Imaging", Brit. J. Radiol., 51: 273 (1978); PA0 Kumar et al., "NMR Fourier Zeugmatography", J. Mag.Res., 18: 69-83 (1975); PA0 Mansfield et al., "Planar Spin Imaging by NMR", J. Phys. C: Solid State Physics, 9: L409-412 (1976); PA0 Edelstein et al., "Spin Warp NMR Imaging and Applications to Human Whole-Body Imaging", Phys Med. Biol., 25(4): 751-6 (1980); PA0 Crooks et al., "Nuclear Magnetic Resonance Whole-Body Imager Operating at 3.5 KGauss", Radiology, 143(1): 169-174 (1982); PA0 Crooks et al., "Method and Apparatus for Rapid NMR Imaging of Nuclear Densities Within an Object", U.S. Pat. No. 4,318,043, Mar. 2, 1982; PA0 Crooks et al., "Method and Apparatus for Mapping Lines of Nuclear Density Within an Object Using Nuclear Magnetic Resonance," U.S. Pat. No. 4,297,637, Oct. 27, 1981.
The known techniques vary in complexity and accuracy as well as in their ability to detect flow rate variations from point to point over a broad area. Unfortunately, they are incapable of focusing on a specific portion of a large area, such as a single blood vessel or a selected capillary region within a cross-section of the human body, to provide quantitative flow data specific to that vessel or region.
The imaging of entire cross-sections by NMR without the generation of flow data is also well known. Several methods of generating such images have been disclosed, but all are directed primarily at providing relative nuclear densities representative of the internal structure of the subject at the instant the imaging is performed. Publications disclosing such techniques include the following:
Summaries of the techniques described in the first five of these publications are given in each of the Crooks patents cited at the bottom of the list. Citations for further publications describing these and other techniques are also found in these patents.
If one could combine NMR flow measurement with NMR imaging to provide quantitative flow data as a function of position in a cross-sectional plane, one would be able to measure flow rates anywhere within an object without interfering with the flow itself. Such a technique would be a major advance in the technology of medical diagnostics since it would permit the determination of blood flow rates anywhere in the body without the use of injections or harmful radiations. One could safely and accurately determine in a direct in vivo manner, for example, the efficacy of blood additives for cardiovascular problems. The treatment of full or partial arterial blockages by the use of catheterization, as a further example, could be advanced enormously by using such a technique to view both the artery and catheter and to measure the rate of blood flow therethrough at the same time. A wide range of other applications will be apparent to those skilled in the art.